The Proliferating Cell Nuclear Antigen (PCNA) is the co-factor of DNA polymerase delta, a Key enzyme in cellular DNA synthesis. Is is required for DNA replication and cell cycle progression. Because of the important role that PCNA plays in proliferating cells and because of some unusual aspects in the structure and function of its gene, we propose to investigate the growth-regulation of the PCNA gene, how growth factors affect it and which trans-acting factors interact with its regulatory elements. This project's goal is a better understanding of the factors that regulate cell cycle progression at the G1/S boundary.